1. Field of the Invention
The present invention concerns contrast agent injection-based mammography systems and their mode of operation.
2. Description of the Prior Art
Digital contrast agent mammography (“contrast enhanced digital mammography”, CEDM) is a technology with different characteristics in which—in contrast to conventional mammography—image data of a positionally fixed (normally compressed) breast can be acquired from different angles, which image data can later be reconstructed into a set of thin slice image exposures at high resolution. Compared to conventional x-ray mammography, tomosynthesis has a number of advantages; in particular, pathological structures can be detected more easily since interference signals due to superimposed tissue portions and artifacts can be reduced.
An iodine-containing contrast agent is normally used in digital full-field mammography. In a typical workflow for contrast agent-assisted digital mammography, initially a first (native) digital mammography exposure is acquired (preferably in two orthogonal planes: cranio-caudal/CC projection, mediolateral-oblique/MLO projection) in order to subsequently inject a contrast agent. Additional contrast agent exposures are subsequently produced as a reference. For this purpose it is essential that the subject (thus the breast) to be examined is located in a stationary position and does not move.
In dual energy tomosynthesis, the second exposure, or the second set of exposures, is executed with a spectrum at different energy than the first native blank exposure. A low-energy excitation typically takes place in the first exposure while a high-energy exposure for the tomoscan is provided for the second exposure. In the presentation of the acquired images the presentation of the glandular tissue (as is otherwise typical in mammography) occurs in the background, and the presentation of the contrast agent and of the contrast agent course in the breast takes higher priority.
In principle, two basic possibilities are provided for the implementation of a contrast agent mammography:
1. digital dynamic subtraction mammography, in which the one first, native blank exposure of the breast is compared with a second, contrast agent-enhanced reference exposure, and
2. dual energy subtraction mammography, in which two exposures with differing energy level are acquired after application of a (normally iodine-containing) contrast agent. The contrast agent enhancement can be depicted based on the different absorption properties arising from this and after logarithmic subtraction of the two exposures.
In the known methods for tomosynthesis (as described above), the contrast agent must initially be dosed and then must also be injected at an optimal point in time. In particular, the contrast agent may not be applied too early, and least of all in what is known as the wash-out phase. Furthermore, the contrast agent must also be dosed correctly. In conventional methods according to the prior art, a problem exists in practice because the dosing of the contrast agent is based only on an “on the spot” manual estimation by the treating physician and thus is frequently underdosed or overdosed. Patient-specific and automatic adaptation of the parameters to be controlled to the execution of the tomosynthesis has disadvantageously not been available in methods from the prior art. An additional problem is also that the point in time of the second exposure (tomoscan) must optimally be done according to the case-specific variables. If the second exposure is executed too early or too late, a sufficient result quality cannot be ensured. This in turn leads to the disadvantage that it, if it is needed, an additional system pass (associated with an increased radiation exposure to the patient) must be implemented again. In order to achieve an optimal significance and image quality, it is necessary to set different parameters for the execution of the tomosynthesis (in particular the dual energy tomosynthesis) in order to control the tomosynthesis process. Parameters include, for example, the contrast agent dosing, the point in time of the contrast agent application, the point in time of the execution of the second tomoscan, the determination of the point in time, and the degree of compression and decompression of the breast. A significant disadvantage of the systems known in the prior art is that a time-controlled and patient-specific control of the tomosynthesis is not possible. Moreover, there is no ability to implement the injector for the injection of the contrast agent and the mammography system synchronously based on the previously detected, patient-specific values.